mysql随机取数据的几种高效率方法

介绍高效的mysql随机数据的方法：

 

1]普通方法, 效率太低

代码如下	复制代码
SELECT * FROM table ORDER BY rand() LIMIT 10;

[2] JOIN的方法：

代码如下	复制代码
SELECT *  FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM `table`) – (SELECT MIN(id) FROM `table`)) + (SELECT MIN(id) FROM `table`)) AS id) AS t2  WHERE t1.id >= t2.id  ORDER BY t1.id LIMIT 10;

再把语句完善一下，加上MIN(id)的判断。我在最开始测试的时候，就是因为没有加上MIN(id)的判断，结果有一半的时间总是查询到表中的前面几行。
完整查询语句是：

代码如下	复制代码
SELECT * FROM `table` WHERE id >= (SELECT floor( RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`)) + (SELECT MIN(id) FROM `table`))) ORDER BY id LIMIT 1; SELECT * FROM `table` AS t1 JOIN (SELECT ROUND(RAND() * ((SELECT MAX(id) FROM `table`)-(SELECT MIN(id) FROM `table`))+(SELECT MIN(id) FROM `table`)) AS id) AS t2 WHERE t1.id >= t2.id ORDER BY t1.id LIMIT 1;

前者花费时间 0.147433 秒
后者花费时间 0.015130 秒